When metallurgically compatible metal surfaces are rubbed together, the metal of one surface can metallurgically, i.e. chemically, bond to the metal of the other surface. Such action, for example, is the basis for friction welding and cold welding. The bond, of course, can be as strong as the metal itself. If one attempts to slide the two surfaces on one another after even minute surface areas are so bonded, the sliding action can cause metal to be pulled away from one of the surfaces. When the metal is pulled away from the surface, that surface is considered galled. The mating surface then has a corresponding bump on it that can produce further galling, or even scuffing and scoring. We refer to such action generally as wear. In any event, sliding movement of the two surfaces will cause friction between them to increase. When friction is extreme, bearing surfaces can even seize together. The rate at which this will occur will, of course, vary with pressure applied during the sliding, surface compositions, surface roughness, etc.
To prevent such problems, one approach is to provide an antifriction and/or score-resistant coating on one or both of the mating metal surfaces. We have found a coating that is highly effective as an antifriction or score-resistant coating on metal surfaces, particularly iron-based alloy surfaces in contact with metallurgically compatible metal surfaces. The coating is hard, tenacious and distinctive. Moreover, it is formed by an unusual process.